Difference between revisions of "Nail" - New World Encyclopedia

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The '''nail plate''' is composed of "closely packed, fully keratinized, multilayered lamellae of cornified cells" (Levit and Boissy 2001). ''Keratins'' are a family of [[fibrous protein|fibrous structural proteins]]; tough and insoluble, they form the hard but [[mineral|nonmineralized]] structures found in [[reptile]]s, [[bird]]s, [[amphibian]]s, and [[mammal]]s. [[Cell (biology)|Cells]] in the [[epidermis (skin)|epidermis]] contain a structural matrix of keratin. As certain skin cells [[cellular differentiation|differentiate]] and become cornified, pre-keratin [[polypeptide]]s are incorporated into [[intermediate filament]]s. Eventually the [[cell nucleus|nucleus]] and [[cytoplasm]]ic [[organelle]]s disappear, [[metabolism]] ceases, and cells undergo a [[apoptosis|programmed death]] as they become fully keratinized. Hard structures are formed by intercellular cementing of fibers formed from the dead, cornified cells.
 
The '''nail plate''' is composed of "closely packed, fully keratinized, multilayered lamellae of cornified cells" (Levit and Boissy 2001). ''Keratins'' are a family of [[fibrous protein|fibrous structural proteins]]; tough and insoluble, they form the hard but [[mineral|nonmineralized]] structures found in [[reptile]]s, [[bird]]s, [[amphibian]]s, and [[mammal]]s. [[Cell (biology)|Cells]] in the [[epidermis (skin)|epidermis]] contain a structural matrix of keratin. As certain skin cells [[cellular differentiation|differentiate]] and become cornified, pre-keratin [[polypeptide]]s are incorporated into [[intermediate filament]]s. Eventually the [[cell nucleus|nucleus]] and [[cytoplasm]]ic [[organelle]]s disappear, [[metabolism]] ceases, and cells undergo a [[apoptosis|programmed death]] as they become fully keratinized. Hard structures are formed by intercellular cementing of fibers formed from the dead, cornified cells.
  
The nail matrix cells differentiate and create the nail plate by flattening, broadening, and by  nuclear fragmentation, with an accumulation of cytoplasmic microfibrils (Levit and Boissy 2001). The keratins in the nail plate are believed to be held in place by surrounding globular matrix proteins with a high concentration of cystine disulfide bonds (rather than calcium, as in bones), creating the rigid structure (Levit and Boissy 2001).   
+
The nail matrix cells differentiate and create the nail plate by flattening, broadening, and by  nuclear fragmentation, with an accumulation of cytoplasmic microfibrils (Levit and Boissy 2001). The keratins in the nail plate are believed to be held in place by surrounding globular matrix proteins with a high concentration of disulfide bonds between [[cystine]] (rather than by means of calcium, as in bones), creating the rigid structure (Levit and Boissy 2001).   
  
 
In humans, the nail plate is about 0.6 millimeters to 1 millimeter in thickness (Levit and Boissy 2001). It is dorsally smooth. The nail bed adheres tightly to the ventral surface of the nail plate and slides along the nail plate via longitudinal folds and grooves formed by a nail bed horny layer.  
 
In humans, the nail plate is about 0.6 millimeters to 1 millimeter in thickness (Levit and Boissy 2001). It is dorsally smooth. The nail bed adheres tightly to the ventral surface of the nail plate and slides along the nail plate via longitudinal folds and grooves formed by a nail bed horny layer.  
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==Culture==
 
==Culture==
 
[[Image:The Ci-Xi Imperial Dowager Empress (9).PNG|thumb|right|200px|[[Empress Dowager]] [[Empress Dowager Cixi|Cixi]] displays long fingernails which reflect her high position in [[Qing Dynasty|Qing]] [[China]].]]
 
[[Image:The Ci-Xi Imperial Dowager Empress (9).PNG|thumb|right|200px|[[Empress Dowager]] [[Empress Dowager Cixi|Cixi]] displays long fingernails which reflect her high position in [[Qing Dynasty|Qing]] [[China]].]]
In western culture, long nails are a symbol of femininity, while short nails are a symbol of masculinity.  Nail decoration is usually limited to females.
 
 
In some [[Asia]]n cultures, men may also grow long fingernails, or only the nail on the [[little finger]], to show that they do not do much manual labor, but instead work in an office setting.
 
 
In the 19th century in the [[Balkans]], [[white-collar]] workers, such as clerks, grew their fingernails long to distinguish them from people in lower classes who worked with their hands (Mckay 1983).
 
  
 +
Nail decoration for aesthetic purposes, for both fingernails and toenails, dates to at least Ancient Egypt (Blakemore and Jennett (2001).
  
 +
In modern western culture, long nails are a symbol of femininity, while short nails are a symbol of masculinity.  Nail decoration is usually limited to females. However, in some [[Asia]]n cultures, men may also grow long fingernails, or only the nail on the [[little finger]], to show that they do not do much manual labor, but instead work in an office setting. In Chinese and Hindu cultures, growing long fingernails has also been a practice, as a sign of leisure and status, since it is difficult to practice manual labor with long fingernails (Blakemore and Jennett 2001). In the 19th century in the [[Balkans]], [[white-collar]] workers, such as clerks, grew their fingernails long to distinguish them from people in lower classes who worked with their hands (Mckay 1983).
  
 
Some [[guitar]] players, notably [[classical guitar|classical]] and [[fingerstyle]] players, will purposely grow long nails on the hand they use to pluck the strings. Their longer nails serve as small, easily-maneuverable guitar [[Guitar pick|picks]]. For some serious musicians, daily nail care can become a mark of pride and dedication.
 
Some [[guitar]] players, notably [[classical guitar|classical]] and [[fingerstyle]] players, will purposely grow long nails on the hand they use to pluck the strings. Their longer nails serve as small, easily-maneuverable guitar [[Guitar pick|picks]]. For some serious musicians, daily nail care can become a mark of pride and dedication.
  
In comparison, [[piano|pianists]] must keep their nails trimmed short to avoid clicking noises on the keys and avoid dangerous situations where in fast passages the nail may be caught under a key and rip off, and most [[string instrument|string]] players, such as [[violin]]ists and [[guitar]]ists, must keep at least the nails on their fretting <!-- not necessarily left hand  —>hand short to allow the strings to be fingered correctly.
+
In comparison, [[piano|pianists]] must keep their nails trimmed short to avoid clicking noises on the keys and avoid dangerous situations where in fast passages the nail may be caught under a key and rip off, and most [[string instrument|string]] players, such as [[violin]]ists and [[guitar]]ists, must keep at least the nails on their fretting hand short to allow the strings to be fingered correctly.
 
 
==Fashion==
 
{{main|Manicure}}
 
 
 
Someone whose occupation is to cut any type of nail, apply artificial nails and care for nails is sometimes called a [[nailist]]. The place where a nailist works may be called a nail salon or nail shop (also "nailshop").
 
 
 
Painting the nails with [[nail polish]] (also known as nail lacquer) is a common practice dating back to at least 3000 B.C.E.
 
 
 
Ornamented fake nails are sometimes used to display designs, such as stars or sparkles, on nails. They are also used to make nails look longer.
 
 
 
== Medical test ==
 
Health care and pre-hospital care providers (paramedics) often use the fingernail beds as a cursory indicator of distal tissue perfusion of individuals who may be in [[Shock (medical)|shock]]. However, this test is now accepted as reliable in young children only.{{Fact|date=June 2007}}
 
  
Procedure: briefly depress the fingernail bed gently with a finger. This will briefly turn the nailbed white; the normal pink colour should be restored within a second or two. Delayed return to pink colour can be an indicator of certain shock states such as [[hypovolemia]].{{Fact|date=June 2007}}
+
Painting the nails with [[nail polish]] (also known as nail lacquer) is a common practice dating back to at least 3000 B.C.E.. Colored and clear nail polish or enamel became popular in the early twentieth century for women (Blakemore and Jennett 2001). Ornamented fake nails are sometimes used to display designs, such as stars or sparkles, on nails. They are also used to make nails look longer.
  
==See also==
 
* [[Leukonychia]]
 
* [[Nail disease]]
 
* [[Hangnail]]
 
  
 
==References==
 
==References==
  
<div class="references-small" style="-moz-column-count:1; column-count:1;"><references/></div>
 
 
* Blakemore, C., and S. Jennett. 2001. ''The Oxford Companion to the Body''. New York: Oxford University Press. ISBN 019852403X.
 
* Blakemore, C., and S. Jennett. 2001. ''The Oxford Companion to the Body''. New York: Oxford University Press. ISBN 019852403X.
  

Revision as of 00:22, 22 November 2007


Anatomy

In anatomy, a nail is a horny epidermal derivative that covers the dorsal tip of the fingers and toes of humans and most primates, and consists of of a flattened, slightly curved translucent plate of the protein keratin that forms largely from dividing cells in the base, and attaches to and slides over a nail bed. In humans, nails are the largest skin appendages (Haneke 2006). Human and primate nails are homologous to vertebrate claws and hooves, and made of the same protein (keratin) found in hair, skin, and horns.

scratch pick up objects

decoration of toenails and fingernails for aesthetic purposes dates at least as far back as Ancient Egypt (


Parts of the nail unit

Fingernails
Toenails

The nail unit, for both fingernails and toenails, is made up of several different structures (Levit and Boissy 2001; ND 2005:

  • Germinal matrix or nail root. Much of this is under the nail fold at the base of the nail plate and thus is not seen, although the distal end is seen in most people as represented by the distal end of the lunula. The germinal matrix is formed from thick epithelium and consists of mostly matrix cells, which differentiate into the nail plate.
  • Nail plate. This is the hard, translucent, flattened portion, composed of keratin, with the proximal area white (lunula), the middle portion firmly adhering to and sliding over the nail bed, and the distal portion as the free edge.
  • Lunula. This is the whitish, half-moon or crescent shape structure visible in the human thumb and big toe.
  • Free edge. The free edge is the part of the nail plate that extends past the finger, which is no longer attached to the nail bed.
  • Nail bed. The nail bed is the adherent connective tissue that underlies the nail plate, often colloquially referred to as the "quick." The nail plate adheres to this bed and flows over it.
  • Nail fold. This is the skin that on the three sides of the nail that frames the nail.
  • Nail frame (perionychium). The perionychium or paronychial edge is the tissue of the finger or toe that overlies the nail plate on the sides.
  • Cuticle (eponychium). The eponychium or cuticle is the fold of tissue at the proximal end of the nail, connecting the skin and the nail plate, and overlapping the nail plate at the base of the nail, providing a waterproof barrier.
  • Hyponychium. This is the attachment between the skin of the finger or toe and the distal end of the nail, which also provides a waterproof barrier.

In common usage the word nail usually refers to the nail plate only.


Nail growth

The growth of the nail plate begins in the germinal matrix' or nail root. The matrix is about 4 to 9 millimeters long in humans, with most under the nail fold (Levit and Boissy 2001). The distal end is visible in most people as the lunula in the thumbs and big toes. Consisting mostly of matrix cells, the matrix gives rise to the nail plate and the nail bed.

The nail plate is composed of "closely packed, fully keratinized, multilayered lamellae of cornified cells" (Levit and Boissy 2001). Keratins are a family of fibrous structural proteins; tough and insoluble, they form the hard but nonmineralized structures found in reptiles, birds, amphibians, and mammals. Cells in the epidermis contain a structural matrix of keratin. As certain skin cells differentiate and become cornified, pre-keratin polypeptides are incorporated into intermediate filaments. Eventually the nucleus and cytoplasmic organelles disappear, metabolism ceases, and cells undergo a programmed death as they become fully keratinized. Hard structures are formed by intercellular cementing of fibers formed from the dead, cornified cells.

The nail matrix cells differentiate and create the nail plate by flattening, broadening, and by nuclear fragmentation, with an accumulation of cytoplasmic microfibrils (Levit and Boissy 2001). The keratins in the nail plate are believed to be held in place by surrounding globular matrix proteins with a high concentration of disulfide bonds between cystine (rather than by means of calcium, as in bones), creating the rigid structure (Levit and Boissy 2001).

In humans, the nail plate is about 0.6 millimeters to 1 millimeter in thickness (Levit and Boissy 2001). It is dorsally smooth. The nail bed adheres tightly to the ventral surface of the nail plate and slides along the nail plate via longitudinal folds and grooves formed by a nail bed horny layer.

As the matrix cells grow, the nail plate is pushed out toward the free edge. In addition, Johnson and Shuster (1993) report that the nail is formed continuously along the nail bed as well as by the germinal matrix, reporting in their study that approximately 79% of the nail thickness was contributed by the nail matrix and 21% by the nail bed.

Levit and Boissy (2001) report that the nail plate of human fingernails grows at an average rate of 0.1 mm per day, with toenail growth one half of that rate. Fingernails require 3 to 6 months to regrow completely, while toenails require 12 to 18 months. The actual growth rate is dependent upon such factors as age, season, exercise level, and hereditary factors. And contrary to popular belief, they do not continue to grow after death; the skin dehydrates and tightens, giving the illusion that the nails grow.


Health and care

Long, manicured nails are a fashion statement.

The growth record of fingernails can show the history of recent health and physiological imbalances, and has been used as a diagnostic tool since ancient times. Major illness will cause a deep groove to form across the nails. Mis-coloration, thinning, thickening, brittleness, splitting, grooves, Mees' lines, small white spots, receded lunula, clubbing (convex), flatness, spooning (concave) can indicate illness in other areas of the body, nutrient deficiencies, drug reaction or poisoning, or merely local injury. Nails can also become thickened (onychogryphosis), loosened (onycholysis), infected with fungus (onychomycosis) or degenerative (onychodystrophy).

Nails can dry out, just like skin. They can also be infected. Toe infections, for instance, can be caused or exacerbated by dirty socks, specific types of aggressive exercise, tight footwear and walking unprotected in an unclean environment.

Manicures and pedicures are health and cosmetic procedures to groom, trim, and paint the nails and manage callouses. They require various tools such as cuticle scissors, nail scissors, nail clippers, and nail files.

Nail tools used by different people may transmit infections.

Biting the nails often indicates internal tension, stress, boredom, hunger, or it may simply be a habit.Nail biting can result in the transportation of germs that are buried under the surface of the nail into the mouth. It may also cause excessive or abnormal wear of tooth enamel[citation needed].

Culture

Empress Dowager Cixi displays long fingernails which reflect her high position in Qing China.

Nail decoration for aesthetic purposes, for both fingernails and toenails, dates to at least Ancient Egypt (Blakemore and Jennett (2001).

In modern western culture, long nails are a symbol of femininity, while short nails are a symbol of masculinity. Nail decoration is usually limited to females. However, in some Asian cultures, men may also grow long fingernails, or only the nail on the little finger, to show that they do not do much manual labor, but instead work in an office setting. In Chinese and Hindu cultures, growing long fingernails has also been a practice, as a sign of leisure and status, since it is difficult to practice manual labor with long fingernails (Blakemore and Jennett 2001). In the 19th century in the Balkans, white-collar workers, such as clerks, grew their fingernails long to distinguish them from people in lower classes who worked with their hands (Mckay 1983).

Some guitar players, notably classical and fingerstyle players, will purposely grow long nails on the hand they use to pluck the strings. Their longer nails serve as small, easily-maneuverable guitar picks. For some serious musicians, daily nail care can become a mark of pride and dedication.

In comparison, pianists must keep their nails trimmed short to avoid clicking noises on the keys and avoid dangerous situations where in fast passages the nail may be caught under a key and rip off, and most string players, such as violinists and guitarists, must keep at least the nails on their fretting hand short to allow the strings to be fingered correctly.

Painting the nails with nail polish (also known as nail lacquer) is a common practice dating back to at least 3000 B.C.E. Colored and clear nail polish or enamel became popular in the early twentieth century for women (Blakemore and Jennett 2001). Ornamented fake nails are sometimes used to display designs, such as stars or sparkles, on nails. They are also used to make nails look longer.


References
ISBN links support NWE through referral fees

  • Blakemore, C., and S. Jennett. 2001. The Oxford Companion to the Body. New York: Oxford University Press. ISBN 019852403X.
  • Haneke, E. 2006. Onychocosmeceuticals. Journal of Cosmetic Dermatology 5(1): 95-100.
  • Levit, E. K., and R. E. Boissy, R. E. 2001. Chapter 6. Basic science of the nail unit. In R. K. Freinkel, and D. T. Woodley. The Biology of the Skin. New York: Parthenon Pub. Group. ISBN 1850700060.
  • Johnson, M., and S. Shuster. 1993. Continuous formation of nail along the bed. British Journal of Dermatology 128(3): 277-280.
  • Haneke E (2006). Surgical anatomy of the nail apparatus.. Dermatol Clin 24 (3): 291-6. PMID 16798426.
  1. ^  Toenail Definition - Medicine.net
  2. ^  American Academy of Dermatology - Nail Health
  3. ^  Nails Guide - Nail Health

McKay, John P., Bennett D. Hill, and John Buckler. 1983. A history of Western society. Boston: Houghton Mifflin Co. ISBN 0395328047.


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